sql: add support for ON UPDATE CASCADE for foreign key references

Enables the addition of the ON UPDATE CASCADE action for foreign keys references.

Major changes in `rowwriter.go`:
* Added a quick check to see if a cascader is required at all (this code is in `cascader.go`). And if not, the normal path is followed.
* When a cascader is required, UpdateRow can only use a single batch per row. Unless we can read from batches without running them, this will be a requirement going forward.
* Added the ability to skip foreign key checks for `InsertRow`.
* Merge the `DeleteRow()` And `deleteRowWithoutCascade()` functions.

Major changes in `cascader.go`:
* Added the new `makeCascader` functions that check to see if a cascader is required at all.
* Of course, added `updateRows()`, which performs all the updates.
* Added the checking of foreign key constraints at the end of a `cascadeAll()` call. This of course

Unlike with deletes, there is more to keep track of when looking for orphaned rows. In the wost case, rows can be updated multiple times. So row A -> B, then B -> C, then C -> D. But we don't want to test the middle states for foreign key violations, and we only want to test A -> D. So this accomplished by storing all transitions and looking forward through these updates to find if a row was updated again. There is potential to improve this using a map of some sort, but that can be done in a further update. The normal case is that there is only a single update and there is a quick path to only check that.

There is also a need to compare the contents two rows. Using the example above, say after A -> B and then B -> C, there needs to be a way to determine that the first B is the equivalent of the second B. To accomplish this, a new function on `tree.Datums` `IsDistinctFrom()` was added that treats nulls as equivalent.

Release note (SQL): ON UPDATE CASCADE foreign key constraints are fully supported

pkg/ccl/sqlccl/csv.go

@@ -596,9 +596,16 @@ func convertRecord(
 			if err != nil {
 				return errors.Wrapf(err, "generate insert row: %s: row %d", batch.file, rowNum)
 			}
-			if err := ri.InsertRow(ctx, inserter(func(kv roachpb.KeyValue) {
-				kvBatch = append(kvBatch, kv)
-			}), row, true /* ignoreConflicts */, false /* traceKV */); err != nil {
+			if err := ri.InsertRow(
+				ctx,
+				inserter(func(kv roachpb.KeyValue) {
+					kvBatch = append(kvBatch, kv)
+				}),
+				row,
+				true, /* ignoreConflicts */
+				sqlbase.CheckFKs,
+				false, /* traceKV */
+			); err != nil {
 				return errors.Wrapf(err, "insert row: %s: row %d", batch.file, rowNum)
 			}
 			if len(kvBatch) >= kvBatchSize {

pkg/ccl/sqlccl/load.go

@@ -302,7 +302,7 @@ func insertStmtToKVs(
 		if err != nil {
 			return errors.Wrapf(err, "process insert %q", row)
 		}
-		if err := ri.InsertRow(ctx, b, row, true, false /* traceKV */); err != nil {
+		if err := ri.InsertRow(ctx, b, row, true, sqlbase.CheckFKs, false /* traceKV */); err != nil {
 			return errors.Wrapf(err, "insert %q", row)
 		}
 	}

pkg/sql/backfill.go

@@ -284,7 +284,7 @@ func (sc *SchemaChanger) truncateIndexes(
 					return err
 				}
 
-				rd, err := sqlbase.MakeRowDeleter(txn, tableDesc, nil, nil, false, alloc)
+				rd, err := sqlbase.MakeRowDeleter(txn, tableDesc, nil, nil, sqlbase.SkipFKs, alloc)
 				if err != nil {
 					return err
 				}

pkg/sql/create_table.go

@@ -266,7 +266,7 @@ func (n *createTableNode) FastPathResults() (int, bool) {
 //    CREATE TABLE foo (a INT, b INT, CHECK (a < 1))
 //
 // Note some SQL databases require that a constraint attached to a column to
-// refer only to the column it is attached to. We follow Postgres's behavior,
+// refer only to the column it is attached to. We follow Postgres' behavior,
 // however, in omitting this restriction by blindly hoisting all column
 // constraints. For example, the following table definition is accepted in
 // CockroachDB and Postgres, but not necessarily other SQL databases:
@@ -467,7 +467,8 @@ func resolveFK(
 		return pgerror.Unimplemented(feature, feature)
 	}
 	if d.Actions.Update != tree.NoAction &&
-		d.Actions.Update != tree.Restrict {
+		d.Actions.Update != tree.Restrict &&
+		d.Actions.Update != tree.Cascade {
 		feature := fmt.Sprintf("unsupported: ON UPDATE %s", d.Actions.Update)
 		return pgerror.Unimplemented(feature, feature)
 	}

pkg/sql/distsqlrun/columnbackfiller.go

@@ -239,7 +239,7 @@ func (cb *columnBackfiller) runChunk(
 				}
 			}
 			if _, err := ru.UpdateRow(
-				ctx, b, oldValues, updateValues, nil /* mon.BytesMonitor */, false, /* traceKV */
+				ctx, b, oldValues, updateValues, nil /* mon.BytesMonitor */, sqlbase.CheckFKs, false, /* traceKV */
 			); err != nil {
 				return err
 			}